“Follow the water.”
That has been the watch-phrase and standing order of stargazers, including astrophysicists and astrobiologists, for decades as they search for life beyond Earth. That"s because liquid water is considered the key ingredient and essential elixir for all biochemistry on Earth.
Just such possibly life-bearing water has been found on a tiny, ice-encrusted moon orbiting the giant, ringed gas planet Saturn.
Scientists reported Friday in the journal Science that Enceladus, a world of only 310 miles in diameter, contains a subsurface “regional sea,” which sloshes above a rocky bottom.
This water seems centered around the south pole of this moon and may be from five to 10 miles deep. That makes its volume similar to that of North America"s largest lake, the appropriately named Lake Superior, according to the Science report.
The Washington Post notes that some sort of liquid had already been predicted inside Enceladus because back in 2005, plumes of water vapor were photographed as they spewed from the South Pole. These plumes were detected by NASA’s Cassini spacecraft. Now, Cassini has not only confirmed the presence of subsurface water, but of the rocky bottom as well.
The solid, rocky sea floor is especially interesting because the interaction between liquid water and rock means that “chemistry” of the type that produces organic molecules is likely to occur.
All of this means that Enceladus must now move to the head of the line as a possible target for space explorations in search of life beyond Earth. No. Human beings will not soon been blasting off for this suburb of Saturn. But robots and drones could relatively soon pass through these known plumes to nail down precisely what may be there.
In any event, Cassini has identified the plumes as containing water vapor, but Cassini is not designed to search for life. Future spacecraft, however, will do just that.
The Daily Mail informs us that the subsurface sea on Enceladus is covered with at least 20 miles of ice, according to the new report. Thus, the deep down water is only inferred. There is no direct evidence thereof.
But! Because during each of Cassini"s now multiple flybys of this world, ever so faint changes in the wavelengths of its radio signals have been detected. These changes are caused by the gravitational pull on Cassini by the denser mass of the supposed water located at its southern pole. (Surprisingly — to me, at least — according to the report, liquid water is denser than frozen ice.)
Also, the moon"s irregular shape is indicative of the presence of water beneath its surface. There is a shallow “dimple,” or depression, at the South Pole, where missing mass is noted. This means that there is likely denser (or more massive) water below, accounting for deformation of the planet’s shape.
“We know the composition of the shell. We know that it’s water ice. So it’s pretty obvious to think that some of the ice is molten and, therefore, if you melt part of the ice, if you transform it, the volume of it reduces, and you create a depression,” said Luciano Iess, professor of space systems at Sapienza University of Rome and the lead author of the Science report, as quoted in the Post.
And of course, there are those telltale plumes belching water vapor far into space. There are other ways, other than geysers, to produce such a thing; but an under-surface salty ocean is the most likely. The plumes are likely created by a deep ocean shooting water spouts up through the many cracks in Enceladus" icy surface.
So what are we looking at here? Is there life on — or inside — this small, cold ball of ice?
There are several unknowns about this moon, principal of which is how long this "underground" sea has existed. As the late astrophysicistmight say, life on Earth required “billions and billions” of years to take hold. And conditions therefor developed oh, so slowly, sporadically, over those billions of years. Have the same conditions, including temporal conditions, obtained for the origin of life on or in Enceladus?
And, then this question must be asked: Just because there may be water -- abundant water, in fact, -- are the other "essentials" for life as we know it present as well?
“Liquid water’s not enough — not enough for the origin of life certainly,” said Carol Cleland, a University of Colorado professor of philosophy, who spoke with the Daily Mail. “You need an energy source so that you can drive thermodynamically uphill processes.”
Chris McKay, a NASA astrobiologist who advocates for a new Enceladus mission, argues that this moon does have the major essentials for life as we know it: Liquid water, energy from tidal forces, and the life-friendly elements carbon and nitrogen — all of which were detected by Cassini as it flew through and photographed the water vapor-laden plumes.
“Carbon and nitrogen are the concrete [elements] — you need them to build,” McKay said. But McKay also offers a strong caveat about the possibility of life on Enceladus:
“It’s the occupational hazard of astrobiology to jump to the conclusion that you want to be true."
Still, wherever on earth there is free-flowing salt water...well....